JP4841046B2 - Multilayer piezoelectric element and injection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer piezoelectric element and an injection device, for example, a multilayer piezoelectric element and an injection device used for a precision positioning device such as a fuel injection device for an automobile and an optical device, a driving element for vibration prevention, and the like. .
[0002]
[Prior art]
Conventionally, in order to obtain a large amount of displacement using the electrostrictive effect, multilayer piezoelectric actuators in which piezoelectric bodies and internal electrode layers are alternately stacked have been proposed. Multi-layer piezoelectric actuators are classified into two types: simultaneous firing type and stack type in which piezoelectric ceramics and internal electrode plates are alternately stacked. Since the laminated piezoelectric actuator is advantageous for thinning, its superiority is being shown.
[0003]
FIG. 3 shows a conventional multilayer piezoelectric actuator. In this actuator, piezoelectric bodies 51 and internal electrodes 52 are alternately laminated to form active bodies 53a, and the active bodies 53a are not formed on the upper and lower surfaces in the stacking direction. An active body 53b is formed to form a columnar stacked body 53. One end of the internal electrode 52 is alternately covered with an insulator 54, and a conductive adhesive is applied and dried on the side surfaces of the active body 53a and the inactive body 53b from above to form a pair of strip-shaped external electrodes. Electrodes 56 are formed, and these strip-like external electrodes 56 are electrically connected to the internal electrode 52 every left and right layers.
[0004]
In this multilayer piezoelectric actuator, a lead terminal 57 is joined by solder 58 to the surface of the lower end portion of the strip-like external electrode 56 joined to the side surface of the inert body 53b.
[0005]
[Problems to be solved by the invention]
By the way, in recent years, in order to secure a large amount of displacement under a large pressure with a small piezoelectric actuator, the number of stacked layers is increased and a higher electric field is applied to continuously drive for a long time. The above-described conventional piezoelectric actuator has a problem that the end of the strip-shaped external electrode 56 is easily peeled off from the side surface of the inert body 53b.
[0006]
That is, a large displacement occurs in the stacking direction in the active body 53a, but no displacement occurs in the inactive body 53b. Therefore, the end of the belt-like external electrode 56 formed across the active body 53a and the inactive body 53b There is a problem that tensile stress or compressive stress in the stacking direction is generated in the portion, and the end portion of the strip-shaped external electrode 56 located on the inert body 53b is easily peeled off. If driving is continued in this state, the strip-shaped external electrode 56 is peeled off from the surface of the active body 53a not only at the end of the strip-shaped external electrode 56 joined to the inert body 53b but also at the portion located on the active body 53a. Thus, when the connection with the internal electrode 52 is released and the drive is continued for a long time under a high electric field and high pressure, a voltage is not supplied to some of the piezoelectric bodies 51 and the displacement characteristics change during the drive. there were.
[0007]
In addition, there is a problem that the lower end portion of the strip-shaped external electrode 56 to which the lead terminal 57 is bonded is particularly easily peeled off due to the lead terminal 57 being pulled for some reason.
[0008]
An object of the present invention is to provide a multilayer piezoelectric element and an injection device that can improve the bonding strength of an external electrode to a columnar laminate.
[0009]
[Means for Solving the Problems]
The multilayer piezoelectric element of the present invention is a columnar laminate comprising an active body formed by alternately laminating a plurality of piezoelectric bodies and a plurality of internal electrodes, and an inert body provided on each of the upper and lower surfaces of the active body. A pair of external electrodes to which the internal electrodes are alternately connected every other layer are bonded to the side surfaces of the external electrodes, and lead terminals are connected to the end portions of the external electrodes bonded to the side surfaces of the inert body. In the multilayer piezoelectric element, a concave groove is formed on a side surface of the inert body to which an end of the external electrode is bonded.
[0010]
In such a multilayer piezoelectric element, the end of the external electrode is adhered to the portion where the concave groove on the side surface of the inert body is formed, thereby improving the bonding strength between the side surface of the inert body and the external electrode. This can generate a large amount of displacement by applying a higher electric field, and even if it is continuously driven for a long time in this state, it is possible to suppress peeling from the end of the external electrode, and the columnar shape of the external electrode Bonding strength to the laminate can be improved.
[0011]
That is, the external electrode extends from an active body that generates displacement to an inactive body that does not generate displacement for the purpose of reliably joining the internal electrode, and the external electrode straddles the active body and the inactive body. The lead terminal must be joined to the end of the external electrode extended to the inert body because the stress is not generated due to the extension of the actuator in the lead terminal connecting portion. Since the end portion of the external electrode is joined to the portion where the concave groove on the side surface of the inert body is formed, the end portion of the external electrode is prevented from peeling from the side surface of the inert body due to the anchor effect. It is possible to suppress the start of peeling from the end of the external terminal.
[0012]
Moreover, in this invention, it is desirable for the depth of the ditch | groove formed in the side surface of an inert body to be 5-100 micrometers. By adopting such a configuration, it is possible to suppress breakage of the inert body and to effectively prevent peeling of the end portion of the external electrode.
[0013]
Further, in the present invention, it is desirable that the end of the internal electrode to which the external electrode is connected is provided with a protruding conductive terminal protruding from the side surface of the columnar laminate every other layer. By adopting such a configuration, peeling of the external electrode from the columnar stacked body can be further suppressed.
[0014]
In addition, the injection device of the present invention includes a storage container having an injection hole, the stacked piezoelectric element stored in the storage container, and a valve that ejects liquid from the injection hole by driving the stacked piezoelectric element. It comprises.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
1A and 1B show an embodiment of a multilayer piezoelectric element comprising a multilayer piezoelectric actuator according to the present invention. FIG. 1A is a perspective view, and FIG. 1B is a longitudinal section along the line AA 'in FIG. (C) is a perspective view showing a part of (a) in an enlarged manner, and (d) is a sectional view showing a part of (b) in an enlarged manner.
[0016]
As shown in FIG. 1, the multilayer piezoelectric actuator of the present invention includes an active body 1a _{1 formed} by alternately laminating a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2, and upper and lower surfaces of the active body 1a _1. On the side surface of the formed columnar columnar laminate 1 a made of the inert body 1 a ₂ , the internal electrode 2 is covered with the insulator 3 every other end of the internal electrode 2 and not covered with the insulator 3. Protruding conductive terminals 5 are provided at the ends of the substrate, and a conductive adhesive is applied and dried on the side surfaces of the columnar laminate 1a so as to embed the protruding conductive terminals 5, thereby forming the external electrodes 4. A lead terminal 6 is connected and fixed to the lower end of the electrode 4.
[0017]
The external electrode 4 is formed from the active body 1a ₁ to the inactive body 1a _2, and a plurality of concave grooves 9 are formed on the side surface of the inactive body 1a ₂ where the lower end of the external electrode 4 is formed. Yes. These concave grooves 9 are formed in parallel with the exposed end of the internal electrode 2 and in an area range slightly larger than the external electrode formation area. The lead terminal 6 is joined to the end of the external electrode 4 located on the inactive body 1a ₂ by solder or the like.
[0018]
The depth d of these concave grooves 9 is 5 to 100 μm. This is because if the depth is within this range, the inert body 1a ₂ is not broken and the bonding strength of the external electrode 4 can be improved. On the other hand, when the depth of the concave groove 9 is shallower than 5 μm, the bonding strength of the external electrode 4 to the inactive body 1a ₂ is low, and when deeper than 100 μm, it is inactive when driven at a high voltage. This is because easy broken at the portion of the groove 9 of the body 1a _2.
[0019]
The width b of the concave grooves 9 in the stacking direction is preferably 5 to 50 μm from the viewpoint of enhancing the anchor effect. Such a concave groove 9 can be formed by dicing or scratching.
[0020]
Incidentally, it has formed the groove 9 only on the side surfaces of the inert bodies 1a ₂ of the lower lead terminals 6 are formed, it may also form a groove on the side surface of the upper inert body 1a ₂ is Of course. Although the formation of the concave groove 9 in a slightly larger area extent than the external electrode formation area, it is of course possible to form the inert body 1a ₂ whole side surface.
[0021]
Furthermore, although the concave groove 9 is formed in parallel with the exposed end portion of the internal electrode 2, it may be formed so as to be orthogonal to the exposed end portion of the internal electrode 2, and further, the concave groove 9 is formed in a lattice shape. It may be formed.
[0022]
The piezoelectric body 1 is made of, for example, a lead zirconate titanate Pb (Zr, Ti) O ₃ (hereinafter abbreviated as PZT) or a piezoelectric ceramic material mainly composed of barium titanate BaTiO ₃ . The piezoelectric ceramics are those piezoelectric strain constant d ₃₃ indicating the piezoelectric characteristic is high is preferable.
[0023]
The thickness of the piezoelectric body 1, that is, the distance between the internal electrodes 2 is preferably 50 to 250 μm. In order to obtain a larger displacement amount by applying a voltage to the stacked piezoelectric actuator, a method of increasing the number of stacked layers is used. However, when the number of stacked layers is increased, the piezoelectric body 1 is too thick. This is because the actuator cannot be reduced in size and height, and on the other hand, if the thickness of the piezoelectric body 1 is too thin, dielectric breakdown tends to occur.
[0024]
An internal electrode 2 is disposed between the piezoelectric bodies 1, and the internal electrode 2 is formed of a metal material such as silver-palladium, and a predetermined voltage is applied to each piezoelectric body 1. It acts to cause displacement due to the reverse piezoelectric effect.
[0025]
A columnar laminate 1a formed by alternately laminating a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 is first composed of a calcined powder of piezoelectric ceramics such as PZT and an organic polymer such as acrylic or butyral. A binder is mixed with a plasticizer such as DBP (dioctyl phthalate) or DOP (dibutyl phthalate) to produce a slurry, and the slurry is piezoelectric by a tape molding method such as a well-known doctor blade method or calendar roll method. A ceramic green sheet to be 1 is produced.
[0026]
Next, a conductive paste is prepared by adding a binder, a plasticizer, and the like to silver-palladium powder, and this is printed on the upper surface of each green sheet to a thickness of 1 to 40 μm by screen printing or the like.
[0027]
Then, a plurality of green sheets each having a conductive paste printed on the upper surface were laminated, and green sheets on which no conductive paste was printed were laminated on the upper and lower surfaces of the laminate, and the binder was removed at a predetermined temperature. Then, it is fabricated by firing at 900 to 1200 ° C.
[0028]
Then, the paste-like conductive terminal 5 is formed by applying a paste containing silver as a main component to the opposing side surfaces on which the external electrodes 4 of the columnar laminate 1a are formed and baking at 700 to 950 ° C. That is, in order to form such protruding conductive terminals 5, glass powder having a softening point of 600 ° C. to 950 ° C. is dispersed in a paste mainly composed of silver, and the paste is used as an external electrode. By performing application and baking on the formation surface of 4, the protruding conductive terminals 5 can be effectively formed.
[0029]
That is, by dispersing the glass component in the paste, the glass is softened during baking, and in this state, silver that is difficult to diffuse in the piezoelectric body 1 diffuses and gathers near the end of the internal electrode 2, and therefore, FIG. A protruding conductive terminal 5 as shown in (c) can be formed.
[0030]
The protruding conductive terminal 5 is formed on a part of the side surface of the columnar laminated body 1 a, is formed in a rail shape, and its length is substantially the same as the width of the external electrode 4. The length of the protruding conductive terminal 5 may be shorter than the width of the external electrode 4.
[0031]
Further, a groove having a depth of 50 to 500 μm and a width of 30 to 200 μm in the stacking direction is formed on the side surface of the columnar laminated body 1a on which the protruding conductive terminals 5 are formed. The insulator 3 is formed by filling a resin, a polyimide resin, a polyamideimide resin, a silicone rubber, or the like.
[0032]
The end of the internal electrode 2 where no groove is formed is connected to the external electrode 4 via the above-described protruding conductive terminal 5. Note that the external electrode 4 may be formed by bonding a plate-like conductive member to the protruding conductive terminal 5 and bonding the plate-like conductive member to the side surface of the columnar laminated body 1a with a conductive adhesive so as to embed the plate-like conductive member. good. In this case, it is desirable that the conductive adhesive has a small elastic coefficient and easily deforms. The joint between the protruding conductive terminal 5 and the plate-like conductive member is, for example, heat treated at 700 to 950 ° C. in a state where a load is applied, so that the main component silver is the protruding conductive terminal 5 and the plate-like conductive member. They can be diffused to each other, and so-called silver diffusion bonding can be performed.
[0033]
When the plate-like conductive member is connected to the internal electrode 2 through the protruding conductive terminal 5 in this way, the protruding conductive terminal 5 is deformed even when the actuator is continuously driven for a long time under a high electric field and high pressure. Since the protruding conductive terminal 5 can sufficiently absorb the stress generated during driving, the disconnection between the external electrode 4 and the internal electrode 2 can be suppressed, and an actuator having excellent durability can be provided.
[0034]
Furthermore, on the outer surface of the plate-like conductive member, a conductive auxiliary made of any one of a mesh of metal, a mesh-like metal plate, a conductive coil, a conductive corrugated plate, or a conductive fiber assembly (wool shape). A member may be formed. In this case, even when a large current is input to the actuator and driven at a high speed, the large current can flow through the conductive auxiliary member, and the current flowing through the external electrode 4 can be reduced. Can prevent local heat generation and disconnection, and can greatly improve durability.
[0035]
Further, the end portions of the internal electrodes 2 are alternately insulated by the insulator 3 every other layer, and the other non-insulated end portions of the internal electrodes 2 are joined to the external electrodes 4 through the protruding conductive terminals 5. Will be.
[0036]
The insulator 3 is preferably made of a material having a low elastic modulus that follows the displacement of the columnar laminate 1a, specifically, silicone rubber or the like, in order to strengthen the bonding with the columnar laminate 1a. It is.
[0037]
As shown in FIG. 1C, the width B in the same direction as the stacking direction of the protruding conductive terminals 5 lowers the resistance of the connecting portion between the external electrode 4 and the internal electrode 2 and is generated when the actuator is driven. From the viewpoint of sufficiently absorbing the stress, it is desirable that the thickness is 1 μm or more and 1/2 or less of the thickness of the piezoelectric body 1. In particular, the width B is desirably 5 to 25 μm.
[0038]
The protrusion height h of the protruding conductive terminal 5 is desirably 1/20 or more of the thickness of the piezoelectric body 1 from the viewpoint of sufficiently absorbing the stress generated by the expansion and contraction of the actuator. The protrusion height h is preferably 15 to 50 μm.
[0039]
Further, the thickness of the plate-like conductive member follows the expansion and contraction of the actuator, and no disconnection occurs between the external electrode 4 and the protruding conductive terminal 5 or between the protruding conductive terminal 5 and the internal electrode 2. Therefore, it is desirable that it is 50 μm or less.
[0040]
The projecting conductive terminal 5 and the plate-like conductive member are made of a metal having conductivity such as silver, nickel, copper, gold, aluminum, or an alloy thereof, and among these, the bonding strength with the internal electrode is strong, Silver is desirable because of its low Young's modulus.
[0041]
In the multilayer piezoelectric element configured as described above, the end portion of the external electrode 4 is joined to the portion where the concave groove 9 on the side surface of the inert body 1a ₂ is formed. can end of the electrode 4 is prevented from being peeled off from the side of the inert body 1a _2, it is possible to suppress the peeling starting from the end of the external terminal 4. Even if an external force acts on the lead terminal 6 and is pulled, the bonding strength of the external electrode 4 is high, so that peeling of the end portion of the external terminal 4 can be suppressed.
[0042]
The multilayer piezoelectric element of the present invention is not limited to these, and various modifications can be made without departing from the gist of the present invention.
[0043]
FIG. 2 shows an injection device according to the present invention. In the figure, reference numeral 31 denotes a storage container. An injection hole 33 is provided at one end of the storage container 31, and a needle valve 35 that can open and close the injection hole 33 is stored in the storage container 31.
[0044]
A fuel passage 37 is provided in the injection hole 33 so as to be able to communicate. The fuel passage 37 is connected to an external fuel supply source, and fuel is always supplied to the fuel passage 37 at a constant high pressure. Therefore, when the needle valve 35 opens the injection hole 33, the fuel supplied to the fuel passage 37 is formed to be injected into a fuel chamber (not shown) of the internal combustion engine at a constant high pressure.
[0045]
The upper end of the needle valve 35 has a large diameter, and has a cylinder 39 formed in the storage container 31 and a piston 41 that can slide. In the storage container 31, the piezoelectric actuator 43 described above is stored.
[0046]
In such an injection device, when the piezoelectric actuator 43 is extended by applying a voltage, the piston 41 is pressed, the needle valve 35 closes the injection hole 33, and the supply of fuel is stopped. When the application of voltage is stopped, the piezoelectric actuator 43 contracts, the disc spring 45 pushes back the piston 41, and the injection hole 33 communicates with the fuel passage 37 so that fuel is injected.
[0047]
【Example】
First, a columnar laminate was produced. The piezoelectric body was formed of PZT having a thickness of 150 μm, the internal electrode was formed of a silver-Pt alloy having a thickness of 3 μm, and the number of stacked layers of the piezoelectric body and the internal electrode was 300 layers. Five concave grooves having a depth d of 20 μm and a width b of 20 μm were formed at intervals of 100 μm on the side surface of the inert body on which the external electrodes were formed by dicing. The formation area was set to be slightly larger than the external electrode formation area.
[0048]
Next, a paste containing silver is applied to the side surface of the columnar laminated body on which the external electrode is formed, and baked at 800 ° C., and the end of the internal electrode exposed on the side surface of the columnar laminated body has the same direction as the laminating direction. A protruding conductive terminal having a width B of 10 μm and a height h of 20 μm was formed. After that, a groove was formed every other end of the internal electrode, and the groove was filled with silicone rubber as an insulator.
[0049]
Next, polyamic acid, which is a polyimide precursor, is dissolved in N-methyl-2-pyrrolidone (NMP) to form a varnish, and 20% by weight of silver powder is mixed, kneaded, and pasted into this varnish. It applied to the predetermined position which forms an electrode, and while evaporating a solvent in the air of 220 degreeC, the curing reaction was caused to form and the external electrode was formed.
[0050]
Thereafter, a lead terminal is joined to the lower end of the positive electrode external electrode and the negative electrode external electrode with solder, and although not shown, silicone rubber is coated around the actuator by a method such as dipping, and further, the positive electrode, A multilayer piezoelectric actuator shown in FIG. 1 was obtained by applying a polarization voltage of 3 kV to the negative electrode and polarizing the entire actuator.
[0051]
As a result of applying a DC voltage of 150 V to the obtained multilayer piezoelectric actuator, a displacement of 40 μm was obtained in the stacking direction. Furthermore, as a result of applying a driving test by applying an AC voltage of 0 to +150 V to this actuator at a frequency of 60 Hz at room temperature, a displacement of 40 μm was obtained when driving up to 1 × 10 ⁹ cycles, peeling of external electrodes, etc. No abnormalities were observed.
[0052]
Further, the present inventor produced a laminated piezoelectric actuator in the same manner as described above except that the depth d of the concave groove was changed to 5 to 100 μm, and applied a DC voltage of 150 V to the obtained laminated piezoelectric actuator. As a result of the application, a displacement of 40 μm was obtained in the stacking direction. Furthermore, as a result of applying a driving test by applying an AC voltage of 0 to +150 V to this actuator at a frequency of 60 Hz at room temperature, a displacement of 40 μm was obtained when driving up to 1 × 10 ⁹ cycles, peeling of external electrodes, etc. No abnormalities were observed.
[0053]
On the other hand, a laminated piezoelectric actuator was produced in the same manner as described above except that the concave groove and the projecting conductive terminal were not formed, and a DC voltage of 150 V was applied to the obtained laminated piezoelectric actuator. Although a displacement of 40 μm was obtained, a drive test was performed by applying an AC voltage of 0 to +150 V to the actuator at a frequency of 60 Hz at room temperature. As a result, a decrease in the displacement was observed after driving 1 × 10 ⁶ cycles. Therefore, when driving was stopped and the actuator was observed, the lower end portion of the external electrode was peeled off.
[0054]
【The invention's effect】
In the multilayer piezoelectric element of the present invention, the end of the external electrode is bonded to the portion where the groove on the side surface of the inert body is formed, thereby improving the bonding strength between the side surface of the inert body and the external electrode. This can generate a large amount of displacement by applying a higher electric field, and even if it is continuously driven for a long time in this state, it is possible to suppress peeling from the end of the external electrode, and the columnar shape of the external electrode Bonding strength to the laminate can be improved. Therefore, even in the case of continuous driving at a high applied electric field and high speed under a high temperature use environment, a multi-layer piezoelectric element having high durability can be provided at low cost without disconnecting the external electrode and the internal electrode.
[Brief description of the drawings]
1A and 1B show a multilayer piezoelectric element of the present invention, in which FIG. 1A is a perspective view, FIG. 1B is a longitudinal sectional view taken along line AA ′ in FIG. 1A, and FIG. The perspective view which expands and shows a part of (b), (d) is sectional drawing which expands and shows a part of (b).
FIG. 2 is an explanatory view showing an injection device of the present invention.
FIG. 3 is a longitudinal sectional view of a conventional multilayer piezoelectric actuator.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Piezoelectric body 1a ... Columnar laminated body 1a ₁ ... Active body 1a ₂ ... Inactive body 2 ... Internal electrode 4 ... External electrode 5 ... Projection-like conductive terminal 6 ... Lead terminal 9 ... Groove 31 ... Storage container 33 ... Injection hole 35 ... Valve 43 ... Piezoelectric actuator

Claims (4)

The internal electrode is further formed on the side surface of a columnar laminate comprising an active body in which a plurality of piezoelectric bodies and a plurality of internal electrodes are alternately stacked, and an inactive body provided on each of the upper and lower surfaces of the active body. A laminated piezoelectric element formed by bonding a pair of external electrodes alternately connected to each other, and connecting a lead terminal to an end of the external electrode bonded to the side surface of the inert body, A laminated piezoelectric element characterized in that a concave groove is formed on a side surface of the inert body to which an end of an external electrode is bonded. 2. The multilayer piezoelectric element according to claim 1, wherein the depth of the concave groove formed on the side surface of the inert body is 5 to 100 [mu] m. 3. The multilayer piezoelectric element according to claim 1, wherein a projecting conductive terminal protruding from a side surface of the columnar laminate is provided at an end of the internal electrode connected to the external electrode. A storage container having an injection hole, the multilayer piezoelectric element according to any one of claims 1 to 3 accommodated in the storage container, and liquid is ejected from the injection hole by driving the multilayer piezoelectric element. An injection device comprising a valve.

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